1. Field of the Invention
The present invention relates to an ink jet recording ink and an ink jet recording method.
2. Description of the Related Art
In the principle of ink jet recording methods, images are recorded on recording media such as paper, cloth or film by discharging liquid or molten solid ink through nozzles, slits, a porous film or the like. A variety of methods such as a so-called electric charge control method in which ink is discharged by utilizing electrostatic attracting force, a method in which ink is discharged by utilizing the vibration pressure of a piezo-electric element, a thermal ink jet method in which ink is discharged by utilizing the pressure generated by forming foam using heat have been suggested as the method for discharging ink. Ink jet recording apparatus ensuing these recording methods can provide images having extremely high resolution.
The following characteristics are required for inks used in these ink jet recording apparatuses:
(1) A uniform image having high resolution and high optical density and having no blotting and no fogging can be obtained on a paper sheet,
(2) The leading end of a nozzle is not clogged with dried ink because such clogging prevents the excellent discharge responsiveness and discharge stability required of the ink jet recording apparatus,
(3) The ink dries quickly on a paper sheet,
(4) The resultant image has excellent fastness, and
(5) The ink has excellent storage stability for a long period of time.
Inks in which a water-soluble dye is dissolved into an aqueous medium such as water, water-soluble organic solvent or the like are mainly used as the ink used for these ink jet recording methods. However, the inks using a water-soluble dye have inferior water resistance and light resistance.
Therefore, to solve these problems, inks in which a pigment is dispersed in an aqueous medium such as water, water-soluble organic solvent or the like have been investigated. Examples of such inks include an ink comprising a high-molecular dispersant together with an anionic surfactant (Japanese Patent Application Laid-Open (JP-A) No. 56(1981)-147868), an ink comprising a high-molecular dispersant together with a nonionic surfactant (Japanese Patent Application Laid-Open (JP-A) No. 56(1981)-147871), an ink in which a treated pigment is dispersed by a surfactant having a HLB of 8 or more (Japanese Patent Application Laid-Open (JP-A) No. 1(1989)-301760), an ink using polyvinyl pyrrolidone and/or polyvinyl alcohol (Japanese Patent Application Laid-Open (JP-A) No. 5(1993) -263029), an ink using as a dispersant a block copolymer (U.S. Pat. Nos. 5,085,698, 5,221,334), an ink using as a dispersant agraft copolymer (Japanese Patent Application Laid-Open (JP-A) No. 6(1994) -100810), an ink using a high-molecular dispersant obtained by copolymerizing a high-molecular dispersant having a hydrophilic portion and hydrophobic portion with a monomer having a nonionic group (Japanese Patent Application Laid-Open (JP-A) Nos. 6(1994)-264017, 6(1994)-306317), and the like. However, these inks can not satisfy all requirements, and in particular, have problems such as deterioration of storage stability due to aggregation of a pigment, clogging in the leading end of a minute nozzle, and aggravation of discharge stability in use for a long period of time.